Many mechanisms, such as diesel engines for example, have parts which cooperate in timed relation to produce a desired result. In diesel engines the cooperative timed relation between the injection of fuel and a selected piston reaching the top dead center of its stroke is called timing. Timing must be set to the manufacturer's specification for optimum service.
The top dead center position of the selected piston is commonly noted by a hole or slot on the periphery of the flywheel. The slot can be seen with the aid of a timing light when the engine is operating at a preselected speed and timing can be measured by an operator.
An edge of the slot is used to trigger electronic equipment which can measure timing. A large slot may introduce error because the edge of the slot may not represent top dead center. It is desirable to measure from the center of the slot and reduce error introduced by slots of varying widths.
It is therefore desirable to have a service tool which automatically measures timing and prevents the introduction of visual error which is often amplified by slots of varying widths. It is also desirable to measure timing at any engine speed.